The invention relates generally to mapping or survey apparatus and methods, and more particularly concerns efficient transmission of survey signals or data from depth level in a borehole or well to the will surface, for analysis, display or recordation; further it concerns efficient transmission of command data from a surface computer unit to the survey tool at depth level in a borehole or well for control of instrumentation operating modes, operating characteristics, or diagnostic purposes; and further it concerns supply of DC power downwardly to the instrumentation via a wireline by which such command signals and survey data or signals may be transmitted upwardly or downwardly respectively.
U.S. Pat. No. 4,459,760 discloses apparatus and methods to transmit sensor data as further disclosed in U.S. Pat. Nos. 3,753,296 and U.S. Pat. No. 4,199,869 that concern the use of angular rate sensors and acceleration sensors in boreholes to derive data usable in determination of borehole azimuth .psi. and tilt .phi.. However, those patents only refer to data transmission in an upward direction in a borehole. U.S. Pat. No. 4,468,863 discloses a method for bidirectional transmission over the wireline so that survey tool operating modes and other characteristics may be altered from the surface when the survey tool is at depth in the well or borehole, however, that patent does not specifically disclose how such data can be communicated to and from the surface of a well, in usable form, and with the unusual advantages of the simple, effective and reliable communication system as disclosed herein.